It has long been assumed that changing weather patterns were what drove woolly mammoths into extinction. As the weather warmed, the arctic adapted mammoths simply couldn’t cope. Increasingly, however, researchers are finding evidence that it was overhunting that drove the majestic giants into extinction.

The most recent evidence that suggests hunting is to blame rather than warming weather, centers around the weaning age of mammoths. Researchers from the University of Michigan analyzed mammoth tusks and found that the animals had ramped up their weaning process.

Wondering why that matters? Evidence from modern-day elephants and other animals suggest that global warming often forces animals to prolonged weaning, while hunting pressures tend to lead to shorter weaning times.

If climate change was at the root of the reason why mammoths went extinct, assuming that the mammoths reacted in the same way as their modern peers, the weaning age should have increased.

Discovering the shortened weaning period

So how did researchers even figure out that woolly mammoths were being weaned earlier? Researchers looked at the isotopic signatures of 15 different juvenile tusks and examined the ratio of nitrogen-15 isotopes to nitrogen-14 isotopes.

This data was then compared with corresponding data from modern day elephant calfs. Researchers found that the ratio of nitrogen-15 to nitrogen-14 decreased in calfs as they were weaned off their mother’s milk and started to eat solid food.

Examining the tusks over a course of approximately 30,000 years, and using the above information on nitrogen isotopes, researchers discovered that weaning times sped up by about three years in the years before the mammoths went extinct.

If global warming were to blame for mammoth extinctions, scientists should have found evidence that mammoths were being weaned at a later stage in their life. Instead, the evidence uncovered pointed to early weaning, and thus hunting, with the weaning period shortening from eight years to five years.

Fifteen different tusks, with many of them coming from Russia, were used in the study. While the evidence is not conclusive, it offers perhaps the strongest proof to date that humans, not weathern patterns, drove the mammoths into extinction.

The research and resulting study was carried out by U-M doctoral student Michael Cherney, and his advisor Dan Fisher, who is the director of the Museum of Paleontology. If Fisher’s name sounds familiar, it’s probably because you heard of his recent efforts to dig up a mammoth skeleton at a local Michigan farm.